Well, Nintendo has answered as to why they won't release the demos to the eShop:
.Earlier this month, Nintendo announced that it has plans to release E3 demos in select Best Buy stores across North America. Because fewer than 10 percent of Best Buy locations will be offering the demos during E3 week, not everyone will get a chance to play the unreleased games… so why won’t the demos come to the Nintendo eShop, for all Wii U owners to experience? Well, according to Nintendo World Report, the reason is because E3 demos don’t always function properly, and no one wants to show off a game that can break, which would probably leave a bad impression on players and viewers alike.
Source: http://mynintendonew...eshop/#comments
Edited by Reversal, 31 May 2013 - 07:40 PM.